more surface area =more boil off?

This may be a dumb question, but my 15 gallon pot came in today and I did a dry run with 7 gallons of water. I finished my hour boil and cooled as if I was actually brewing and had 5 gallons And a little over a quart left (5 cups to be exact). While doing the same test with my 30 at Turkey fryer and boiling about 6 gallons I only lost 5 quarts. Would it be safe to assume that because of the massive increase in surface area of the boil I'm losing almost 1.75 gallons an hour? That seems like a lot because if my math is right I'm losing just shy of 25% on an hour boil. Thoughts?

You betcha! The more surface area exposed to the air the higher your boil off.
Other factors that can contribute to more boil off are strong wind and low humidity. You just have to get a feel for the boil off in your new vessel and build it into your pre-boil volume calculations, that's all.

I also have a 15 gallon pot (megapot), and can lose almost 2 gallons/hr. I usually just estimate 1.75 gallons loss. My boil off varies some, depending on wind hitting the flame, and the weather. It's always in that 1.5 to 2 gal/hr range though.

This should make.my first all grain session on Saturday interesting... might as well shoot for a pre boil volume of atbleast 7 gallons and if I have too much wort just keep it rolling

veritas524 said:

This should make.my first all grain session on Saturday interesting... might as well shoot for a pre boil volume of atbleast 7 gallons and if I have too much wort just keep it rolling

Click to expand...

7 gallons is a pretty good number. Many brewers try to get a bit over 5 gallons into the primary fermenter so when they rack off and leave the trub behind they get 5 gallons of finished beer.

Be aware that if you don't boil off as much as you thought and you decide to "keep it rolling" it will change your hop utilization rates and may make your beer more bitter than the recipe intended. The longer hops are in the boil, the more bitterness they extract. Particularly late hop additions intended for flavor and aroma may end up extracting a lot more bitterness than the recipe intends if you boil longer.

In addition to adding to bitterness, you won't get the aroma or flavor you were expecting due to boil off of the light hydrocarbons.

Think of it this way if you add 10 minutes to your boil, your 60 addition becomes a 70 (not a huge difference in utilization) but your 10 minute add becomes a 20 minute addition (totally different), and that 1 minute add, well that just became a 10. You get the picture.

Frodo said:

I also have a 15 gallon pot (megapot), and can lose almost 2 gallons/hr. I usually just estimate 1.75 gallons loss. My boil off varies some, depending on wind hitting the flame, and the weather. It's always in that 1.5 to 2 gal/hr range though.

Click to expand...

I too have the 15 gallon megapot. I was surprised at how much I lost in the boil my first run, about 2 gallons. wish I would have done a test run with water first

Some great info to know. I will be getting 7 gallon pot soon.

If you mark your pot with graduations, you can determine your end volumes with simple algebra during your boil.
The flavoring and aroma hops can be backed up if needed and I'd just roll with the bittering addition. The IBU difference after 60 minutes is very minor.

Good luck,
Bull

bullinachinashop said:

If you mark your pot with graduations, you can determine your end volumes with simple algebra during your boil.
The flavoring and aroma hops can be backed up if needed and I'd just roll with the bittering addition. The IBU difference after 60 minutes is very minor.

Click to expand...

+1. A few minutes before you're going to be adding any later hop additions, measure what your boil off has been, then adjust the time of the additions if necessary. That 60 minute addition isn't nearly as important timing-wise as the taste and aroma additions.

I need to go get a new paddle/spoon at lunch today to mark. My old one is all carved up for my other pot. Only thing that concerns me is if I should mark it for when the water is hot or "cold." There is a lot of expansion that occurs isn't there?

I believe the volume is about 4% larger at boiling compared to about 70F. That's the ballpark I believe. So 7 gallons at boiling is closer to 6.7 gallons at 70F.

bullinachinashop said:

If you mark your pot with graduations, you can determine your end volumes with simple algebra during your boil.

Click to expand...

I prefer to let the Internet think for me I use a yardstick instead of graduations.

-Joe

Nice link Nostalgia. I've never seen that web page. Probably wouldn't be too hard to just throw that all in an excel sheet either for when you have a laptop but no internet access.

hah, i just did this tonight. see my results in my post in this forum. i started with 7 and ended up with 4.75 gallons of water, leaving me two quarts to play with including solids from steeping and liquid extract. That's after cooling to 75 degrees from the boil.

I have a 39 quart pot.